1. Field of the Invention
The present invention relates to the engine industry, particularly engine fuel systems to fuel powered engines, and more specifically to a fuel system and method for reducing vehicle hydrocarbon emissions.
2. Description of Related Art
Since as early as 1942, particularly in urban areas having a high concentration of motor vehicles, air pollution from internal combustion engines has been recognized as an undesirable consequence of a mobile society. Emissions from the internal combustion engines arise from several sources and can vary considerably in both amount and composition depending on the engine type, operating point, condition, design, and fuel volatility. For engines without some form of emissions controls, it has been estimated that twenty to twenty-five percent of the emissions arise from crankcase ventilation, sixty percent from exhaust, and the rest from evaporative losses, primarily associated with the fuel tank. The exhaust gas of the internal combustion engines contains various amounts of unburned hydrocarbons, carbon monoxide and oxides of nitrogen.
During recent years, researchers have investigated extensively various means of reducing exhaust emissions. This research has been quite fruitful. As a result, present-day automobiles emit only a fraction of undesirable materials compared to those of less than a decade ago. Despite such tremendous advances that have been made, further improvements are desirable. Federal standards continue to require further reduction of emissions. A major obstacle in achieving further reduction in exhaust emissions is the fact that in modern vehicles, 60-95% of hydrocarbon emissions occur during the first 30-90 seconds of operation of a vehicle engine following a cold start.
Applicants recognized that there are several factors that contribute to excess hydrocarbon emissions at low engine temperatures. One of the primary factors is poor vaporization of a sufficient fraction of the fuel at start-up temperature (i.e., below 30° C.) to achieve stable combustion necessitates a generous over-fueling during the cranking and warm-up periods. The over-fueling leads to high engine-out hydrocarbon emissions. This problem is exacerbated as a result of significant over-fueling because the emission system catalyst (i.e., catalytic converter) does not achieve its optimum operating temperature until 1-2 minutes after a cold start, and thus, it is incapable of oxidizing all of the unburned fuel including that resulting from the generous over-fueling during start-up.
In the past, attempts have been made to eliminate the need for a warm-up period by operating the engine on liquid petroleum gas, or other gaseous secondary fuels, during the warm-up period and then switching to gasoline after a normal operating temperature is obtained. The concept was used, for example, on tractors and other machinery. These devices had a separate fuel tank that was filled with a second type of fuel different from the fuel in the main tank. The fuel supply was then selected with a manually operated petcock valve. These systems were shown to be somewhat impractical, however, because the customer is required to fill two tanks, and the distribution network for dispensing gaseous fuels into vehicles is relatively sparse. Plus, customers would have to learn new behaviors and become comfortable with new safety procedures. Both are actions that consumers generally find unacceptable.
Due to the difficulties and impracticalities of using two separate fuels and two fuel source systems, other systems were developed which separated a single fuel into two components, one being more volatile than the other one. The systems, however, still had limitations, including the initial use of the primary fuel remaining in the fuel line at start-up, undesirable delays in starting the engine, the need for additional or complex pressurization and heating systems, efficient production of the volatile fuel, undesirable fuel tank heating resulting in increased evaporative emissions, and/or the use of complicated and expensive components.
The On-Board Distillation System (OBDS) described in U.S. Pat. No. 6,119,637, titled “On-Board Gasoline Distillation for Reduced Hydrocarbon Admission at Start-Up” by Matthews et al. and assigned to the assignee, incorporated herein by reference in its entirety, was developed to address the cold-start emissions issue by utilizing a vapor separator to extract, from gasoline or a gasoline/alcohol blend, etc., a highly-volatile secondary fuel for exclusive use during starting and warm-up, and purging the fuel lines with such secondary fuel prior to engine restart. OBDS was credited with increasing the amount of desired components by volume in the secondary fuel from 20-25% delivered by prior systems to up to approximately 50% or so. The special secondary start-up fuel helped eliminate the need for start-up over-fueling. The system, however, was primarily developed for fuel systems having an engine to fuel tank return line. Further, the system was generally configured to recycle primary fuel to further extract additional secondary fuel not extracted on a first pass through the vapor separator.
Therefore, recognized by the Applicants is a need for an even less complicated and less expensive system that more efficiently separates fuel into it various components to produce a secondary fuel having a composition by volume of between 80-100% desired components, provides an improved air-fuel mixture at engine start-up, provides for enhanced catalyst heating, reduces operating energy requirements, reduces any inherent increase in evaporative emissions, and, as a result, reduces total hydrocarbon emissions over that of prior systems.